The Innocent

Season 4, Episode 6:

A terror attack is planned on the UK transport system, orchestrated by an Algerian terrorist, Malek, whilst locked in a high security prison cell. The team choose the unorthodox and risky strategy of freeing Malek so that he will lead them to the cell before the attack occurs. As they mount surveillance on Malek and his civil liberties lawyer, they discover that Malek is not the terrorist they thought he was but simply an innocent man and his arrest the result of a Special Branch admin error. However, since Malek's release he has been meeting known terrorists -- has Malek been turned while in prison? Adam interrogates Malek and discovers Malek's family are being held hostage until Malek commits the required act of terror. The team fight to save Malek's innocence but risk his family's lives in the process.